Cerebellar Purkinje Cell
Projection to the Peripheral
Vestibular Organ in the Frog
Abstract. Neurones located 200 to
300 microns from the surface of the
auricular lobe of the frog cerebellar
cortex, and identified as Purkinje
cells, were activated antidromically
from the eighth cranial nerve. A parallel anatomical study confirmed the existence of this projection. On the basis
of these findings the existence of a
cerebello-vestibular efferent system is
postulated, the precise significance of
which is as yet unclear. However, since
Purkinje cells in other species have
an inhibitory action on their target
cells, the Purkinje efferent system to
the vestibular organ may have an ac-
tion similar to that ascribed to the
olivo-cochlear bundle upon the cochlea,
that is, to serve as an inhibitory control system.
An outstanding characteristic of the
neural organization of the cerebellum
throughout evolution has been the presence of only one efferent system from
the cerebellar cortex—the Purkinje cell
axons. While most of these axons project directly to the underlying cerebel-
with micropipettes filled with 444 NaCl
ascribed to the antidromic invasion of
Purkinje cells (7, 12).
and 3M KCI, respectively. The average
direct-current resistance of the extra-
Giant extracellular positive-negative
cellular recording electrode was 5 meg-
action potentials were recorded from
the frog auricular lobe after threshold
electrical stimulation of the eighth
nerve (Fig. 1, B and C). Four criteria
were used to identify these action po-
ohms; that of the intracellular one was
10 megohms. As in previous experiments (8), the threshold current for
electrical stimulation of the eighth
nerve was measured attheinitiation of
the experiment and was neverincreased
above 2.5 times threshold.
Electrical activation of the eighth
nerve evokesactivation of Purkinje cells
in the frog auricular lobe via climbing
and mossy fibers (8). The activation
of cat (9) and frog Purkinje cells (70)
by climbing fibers has been characterized by an all-or-none burst. of spikes
having a very regular pattern of discharge and an almost constant latency.
Activation by mossyfibers, on the other
hand, produces, in the cat, activation
of Purkinje cells which has variable
tentials as those generated by Purkinje
cells: (i) their antidromic activation
from extracerebellar regions (6, 10, 12,
13), (ii) their characteristic large extra-
cellular action potentials, the so-called
“giant spikes” (73), (iii) their ortho-
dromic activation by stimulation of
parallel fibers (7, 10, 14), and (iv) in
the auricular lobe, their depth from the
piaglial membrane, that ‘is, 200 to
300 » from the surface (8). Forty-seven
cells were studied; their latency is illustrated in Fig. 1K. A large numberof
Purkinje cells activated at longer latencies were not included since their
latency (71). Similar findings have been
reported for the frog cerebellum (7, 8.
12), Our report, however, deals almost
latencies put them outside the scope of
tion of short latency, which has been
tion of the eighth nerve (Fig. 1K). The
exclusively with Purkinje cell activa-
this paper.
There appear to be two groups of
action potentials activated by stimula-
G
lar nuclei (7, 2), anatomists have de-
scribed many extranuclear projections
in different species (2, 3). Recent physi-
neat
=x
ological evidence has confirmed the
existence of these extranuclear projections (4) and, in addition, has shown
that Purkinje cells have an inhibitory
E
action on cerebellar and vestibular nuclei (4). Furthermore, the axon collaterals of Purkinje cells are inhibitory
on cerebellar basket cells (5) and di-
I
(fe
F Ke
So far, however, the cerebellar pro-
mary sensory systems. Our experiments,
on the other hand, indicate that, in the
frog, auricular Purkinje cells project
directly to the peripheral vestibular
organ.
The general experimental procedures
have been described (7, 8). Bullfrogs
(Rana catesbiana) were anesthesized
with pentobarbital sodium (60 mg per
kilogram of body weight), and the
eighth nerve was stimulated electrical-
ly by means of bipolar electrodes lo-
cated extracranially in its anterior or
posterior branches (Fig.
cellular
and
intracellular
1A). Extra-
recordings
from Purkinje cells were performed
1328
|
——
4
jections described have been restricted
between cerebellar efferents and pri-
4h
J
rectly to Purkinje cells themselves (6).
to systems involved in motor control,
no direct relation having been found
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Fig. 1. (A) Diagram of frog brainstem, labyrinth, and experimental arrangement; BC,
bipolar ganglion cells; CER, cerebellum; CF, climbing fiber; GC, granule cell; ME, recording microelectrode; MF, mossy fiber; OL, optic lobe; PC, Purkinje cell; RC, receptor cell; .S, peripheral nerve stimulating electrode; V, trigeminal nerve; VI/, facial nerve;
VIII, stato-acoustic nerve; PB, posterior branch; arrows indicate the direction of impulse conduction. (B~F) Antidromic extracellular action potentials from Purkinje cells
in the auricular lobe, recorded at a depth of 250 » and evoked by stimulation of the
eighth nerve.
(B and C)
All-or-none spike
responses
at threshold
intensity from
two different Purkinje cells. (D-F) Purkinje cell action potentials evoked by activation
of the eighth nerve at 1.3 times the threshold. (D) Control. (E) Refractory
period for antidromic invasion of the Purkinje cell after double shocks with a short
interval between stimuli. (F) As in E, but with longer interval between stimuli, showing second Purkinje spike. (G and H) Extracellular and intracellular recording from
a Purkinje cell in the auricular lobe at a depth of 300 » activated antidromically and
synaptically by stimulation of the eighth nerve. (G) Extracellular record. (H and I)
Intracellular records of the same cell showing the antidromically excited action potential and an excitatory postsynaptic potential. (J) At slightly higher stimulus intensity
the Purkinje cell shows also a transsynaptic response. (K) Latency histogram of the
early spike responses after stimulation of the eighth nerve. Abscissa, time in milliseconds. Ordinate, number of Purkinje cells recorded. The arrows in B-J indicate stim-
ulus artifact location. Time and voltage calibration as indicated. The polarity is ex-
pressed by the positive and negative signs on the amplitude calibrating bar.
SCIENCE, VOL. 158